Results from soybean nutrient management trials

Starter N application is commonly practiced in the northern U.S. and High Plains soybean production areas and is of particular interest in high residue situations.

Two sets of field trials were conducted to evaluate soybean response to nutrient management and other practices. The “starter/foliar” and “high yield” trials were conducted on-farm at the four 2011 Soybean Management Field Day sites near Bancroft, Elba, Clay Center (SCAL), and Cortland (Table 1). All sites were in corn in 2010 and rotated to soybean in 2011. Crop residue cover of soil was 95% at Bancroft and 45-65% elsewhere. All trials were planted in early May, but cool weather delayed seedling establishment.

Starter N application is commonly practiced in the northern U.S. and High Plains soybean production areas and may be of particular interest in high residue situations. Injection of 15 lb/ac N two inches to the side of the row resulted in a 6% yield increase in Brookings, S.D.

Foliar nutrient application is much promoted but previous research showed a low probability of profitable response from its use compared to traditional, well-managed soil fertility. New products such as those with slow release N may be effective and needed to be evaluated.

In addition, growth promoters and other practices used alone or in combination with other practices may be effective in increasing yield in already high-yield situations.

Starter/Foliar Trial

Treatments were:

1) control with no starter N, foliar application, or row cleaning2) row cleaning only 3 & 4) 5 or 10 lb/ac N in-furrow5 & 6) 10 lb/ac N injected two inches to the side of the seed furrow or applied over the row7, 8 & 9) foliar N application at V4, R2 (full bloom), or both at V4 and R210) starter plus foliar N application at V4 and R2

Planting was in 30-inch rows at about 150,000 seeds per acre, and without row cleaning, except for treatment 2. Starter N was applied as UAN diluted with water to reduce risk of seedling damage. The foliar treatment was a combination of Nachurs N-Rage (N-P-K 23-4-2 with 0.05% Mn; the N is 67% triazone; rate = 2 gal/ac) and Nachurs SoyGrow (0.36% Fe, 0.5% Mg, 2.6% Mn, and 1.5% Zn; rate = 1 pt/ac).

Early plant growth was not affected by starter N application except at the high-residue Bancroft site where early growth was increased with 10 lb/ac N injected in-furrow or 2-inch to the side of the row. However, this did not result in increased yield. Mean yield was two bu/ac more with foliar application at R2 compared with the control, but other treatments had no effect on yield at all locations (Table 2).

High Yield Trial

Five practices were evaluated for their effect on soybean yield:

Breaking apical dominance at V2 to increase branching and pod number

Applying 5 lb/ac starter N in furrow with split emitters

Applying foliar nutrient NPK + micronutrient (as above) at R2

Adding BioForge seed treatment at 4 oz/cwt

Adding Optimize 400 seed treatment

This was an omission or minus-one trial so that the effect of practices could be tested in the presence of all other practices.

Treatments included:

None of these practices used

A full package with all five practices used

Five treatments which consisted of the full package minus one of the above five practices.

Full package with plants clipped at the second trifoliate stage to break apical dominance replaced by a 12 oz/ac lactofen “Cobra” application

The sites were tilled and planted in 20-inch rows. A strobilurin fungicide was applied at R2 and 25 lb/ac N was soil applied at R3 (beginning pod development) for all plots.

Starter N was applied as diluted UAN in furrow by injecting 5 lb/ac N in the seed furrow using split emitters to minimize N contact with the germinating seed and avoid seedling injury. Foliar nutrient application was as above at the R2 growth stage. Seed was treated with BioForge at 4 oz per 100 cwt to promote vigorous early root growth for improved nutrient and water uptake. Seed was treated with Optimize 400 to promote plant growth and ensure good nodulation for N fixation.

The effects of these practices were consistent for all locations. Clipping and Cobra (lactofen) application reduced yield (Table 3). The other treatments had no positive or negative effect on yield.

Findings

Mean yield was 66 bu/ac in the starter/foliar trial and less in the high yield trial. Treatments had little or no effect on yield and these results from four locations should discourage use of all the practices tested, especially clipping or Cobra application to break apical dominance. Still, it is possible that some of the practices tested may be useful in much higher yield situations.

Further evaluation of the foliar nutrient application at R2 is justified. NRage and Soygrow might be tested separately to confirm the yield increase and determine which nutrients might cause the yield increase.

Starter N application had a good test at Bancroft where crop residue cover was heavy and cool weather followed planting. While some starter N treatments enhanced growth, this did not translate to increased yield.

Treating seed with Bradyrhizobia inoculum is encouraged where soybean has not been grown for four or more years or where flooding occurred, but the results do not support routine inoculation for the corn-soybean rotation.